Carbon fibers constituting the carbon fiber bundle have a superior specific strength and a superior specific modulus as compared to other fibers. Furthermore, the carbon fibers have a number of excellent characteristics such as a superior specific resistance and higher chemical resistance as compared to metals. Hence, the carbon fiber bundle is widely used in the sports field, the aerospace field and the like as a reinforcing fiber for composite materials with resins utilizing its various excellent characteristics.
The carbon fiber bundle is usually obtained by heating (carbonization treatment) a flameproofed fiber bundle, which is obtained by heating (flameproofing treatment) a carbon fiber precursor fiber bundle (precursor yarn bundle) such as polyacrylonitrile or rayon at from 200 to 300° C. in an oxidizing atmosphere, at from 800 to 1500° C. in an inert atmosphere such as nitrogen or argon. Furthermore, this carbon fiber bundle is also heated (graphitization treatment) at from 2000 to 3000° C. to manufacture a carbon fiber bundle which exhibits a higher modulus of elasticity in tension, namely, a graphite fiber bundle. In these carbonization treatment process and graphitization treatment process, in many cases, a great number of fiber bundles are arrayed and conveyed into a carbonization furnace and a graphitization furnace simultaneously in order to increase the production efficiency.
Typically, each of the carbonization furnace to perform the carbonization treatment and the graphitization furnace to perform the graphitization treatment consists of a heat treatment chamber corresponding to a furnace body to perform the heating of the fiber bundle in an inert atmosphere and a sealing chamber which is configured to maintain the inert atmosphere of the heat treatment chamber and furnished to each of a fiber bundle inlet (inlet portion) and the fiber bundle outlet (outlet portion) provided in the front and back of the heat treatment chamber.
Specific roles of the sealing chamber is mainly to prevent the reaction gas generated from the fiber bundle in the heat treatment chamber from flowing out to the outside via the fiber bundle inlet or the fiber bundle outlet of the heat treatment chamber as well as to prevent a decrease in quality and grade of the carbon fiber bundle as oxygen enters the heat treatment chamber from the outside and thus the inside of the heat treatment chamber is in an oxidizing atmosphere. The running fiber bundle is contaminated by the tar-like substance formed when the outflowed reaction gas is cooled in some cases, particularly when the reaction gas from the heat treatment chamber is flown out to the vicinity of the inlet or outlet of the furnace.
In addition, an inert gas is supplied to the sealing chamber in order to maintain the inert atmosphere by sealing the heat treatment chamber, but the unevenness in supply of the inert gas leads to not only the unevenness in atmosphere in the sealing chamber but also the unevenness in atmosphere in the heat treatment chamber.
On the other hand, an increase in productivity and a decrease in cost have been required to the recent technology for manufacturing the carbon fiber bundle, and significant improvements have been achieved. For example, improvements such as the highly dense array to array and heat treat a great number of fiber bundles at the same time by increasing the mechanical width of the heat treatment chamber (width of the heat treatment chamber allowing the fiber bundle to run) or a multistage treatment to increase the number of stages of the fiber bundle to be simultaneously heat treated. In such a situation, the unevenness in atmosphere in the sealing chamber caused by the unevenness in supply of the inert gas leads to the occurrence of the unevenness in heat treatment of the fiber bundle or the inhibition on the inert atmosphere maintenance in the heat treatment chamber in some cases. As a result, the unevenness in supply of the inert gas in the sealing chamber causes the unevenness in quality of the carbon fiber bundle and thus becomes a major obstacle in improving the productivity of the carbon fiber bundle in some cases.
A method is proposed in Patent Document 1 in which the inert gas which has been heated in advance is injected through the injection port using a carbonization furnace equipped with a heat treatment chamber, an inert gas injection port, and an inert gas introducing member to introduce the injected inert gas into the direction of the heat treatment chamber so as to prevent the contamination of the fiber bundle.
In addition, a sealing mechanism is proposed in Patent Document 2 which is superior in maintainability by having a removable structure while adopting the labyrinth structure. As the method of supplying the inert gas, a method is proposed in which the inert gas passes through at least one or more perforated plate and thus is jetted out in sheet form.